1. FIELD OF THE INVENTION
This invention relates to antennas employing a single or multitude of slot-type radiators in a conductive medium, wherein the state of radiation for single or selected groups of radiators is altered to thereby provide selected radiation patterns.
2. RELATED ART
Antenna arrays and phase-scanned antenna arrays are well known. An array is a multitude of radiators, not necessarily in a regularly spaced arrangement. Each radiator is not always identical to the other. Typically, the arrays provide a selected set far-field pattern by varying the phase of the electromagnetic energy fed to selected radiating elements. Scanning involves rotating a given far-field pattern in space, usually in a selected plane. A slot-type radiator is usually an opening in a conductive medium, whereby electromagnetic energy is radiated from the opening, most often shaped like a rectangle, ring, "Y" or cross. Such radiator can be similar to an implementation where the dipole equivalent of a slot is realized as a dielectric shape on a background of material of a different dielectric constant.
Chamberlin, in U.S. Pat. No. 3,345,631, discloses a phased array radar scan control. Chamberlin applies phase shifted pulses to rows and columns of slot radiators to vary the phase of the electromagnetic energy at each slot and thereby scan the antenna beam.
Lindley in U.S. Pat. No. 3,604,012 switches the radiative state of selected coupled pairs of slots to reverse the phase of the energy radiated by the pair and thus scan an antenna beam.
Nemit in U.S. Pat. No. 3,969,729 spaces radiator slots a quarter of a wavelength apart to provide various phase states for each radiator "element". The net phase of the aperture of the element is set to one of the possible phase states by opening selected slots in the element. Nemit uses his elements in phase scanned arrays.
When scanning a far-field pattern, distortion is generally increased as the pattern is moved from broadside, but the general far-field pattern is preserved. The aperture size is also generally preserved during scanning
Not disclosed in the related art is an array which can scan very fast and shift pattern footprints fast as well as allow for large changes in operating frequency, that is, an array which can quickly shift the relative amplitude and position of the main beam(s) and side lobes as well as scan by rotating a particular radiated pattern. Further, the related art does not provide an array which can quickly vary the aperture size and thus sharpen and intensify the far-field pattern. This technique also has potential for a low recurring-cost design.